Rules of Hex
Shape of the board
The Hex board is composed of hexagons, arranged in an n × n rhombus, where n is an integer greater than one. Thus Hex can be played on boards of different sizes, and which size is considered standard varies. Piet Hein used a board of size 11, while John Nash settled on size 14. Nowadays people usually use the sizes that are available on game sites on the Internet offering Hex. Games.wtanaka.com uses sizes 11, 14 and 19; Little Golem offers the sizes 13 and 19. (See the article Board size for more.)
It is also possible to play on boards of size m × n where m and n are distinct integers, but in this case a winning strategy is known for the player with shortest distance between his sides.
This is how a typical Hex board looks:
Playing the game
Hex is played by two players, who take turns placing pieces on the board. The players have different colours, say red and blue. (The players themselves are sometimes referred to as Red and Blue) The four edges of the board are coloured with the same colours, in such a way that parallel edges have the same colour. Red wins if he can build a continuous chain between the two red edges, and blue wins if he can build such a chain between the blue edges.
Example: the following diagram shows a game after the first three moves.
The next diagram shows the rest of the game.
Red has won this game, since he has built a connection from the top to the bottom.
The swap rule
The above rules give a strong advantage to the first player. Because of this, the swap rule (also called the Pie rule) was introduced. Suppose that Red is to make the first move. Then the first player places a Red piece on the board, in any cell he likes. After that, the second player decides who will play Red and who will play Blue. Then whoever was decided to be blue makes the next move, and the game continues normally (that's how it works at games.wtanaka.com and pbmserv).
Another possibility to swap (without changing sides of each player) is to make a piece swap. That is, the second player in his first move may remove the first stone which was placed on field with coordinates (x;y) and place his/her own stone on field (y;x). That's how it works at Little Golem. These two ways of swapping are effectively the same.
Beyond the rules
For more information on how best to utilize the rules, see Strategy.